Search results for "clone"

Effect of Unidirectional Vertical Wind Shear on Tropical Cyclone Intensity Change—Lower‐Layer Shear Versus Upper‐Layer Shear

2019

Dust emissions in the West African heat trough the role of the diurnal cycle and of extratropical disturbances

2008

The summertime West African heat trough (HT) is one of the most active dust sources in the world. A detailed case study during May/June 2006 based upon analyses from the European Centre for Medium-Range Weather Forecasts and a new Meteosat dust product illustrates two important mechanisms of dust emissions in this region: (1) The dry continental-scale HT circulation exhibits a strong diurnal cycle characterized by nocturnal low-level jets and downward mixing of momentum to the surface during the build-up of the planetary boundary layer in the morning. This leads to strong gusty surface winds and dust emission, mostly along the northern side of the HT, but also within the southerly monsoon f…

In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone - Part 2: NPF inside ice c…

2021

From 27 July to 10 August 2017, the airborne StratoClim mission took place in Kathmandu, Nepal, where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New particle formation (NPF) was identified by the abundant presence of nucleation-mode aerosols, with particle diameters dp smaller than 15 nm, which were in-situ-detected by means of condensation nuclei (CN) counter techniques. NPF fields in clear skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere–lowermost stratosphere (UTLS) levels and within the Asian monsoon anticyclone (AMA). NPF-generated nucleation-mode particles in elevated concentration…

Northern Hemisphere extratropical cyclones: A comparison of detection and tracking methods and different reanalyses

2008

Abstract The applicability of three different cyclone detection and tracking schemes is investigated with reanalysis datasets. First, cyclone climatologies and cyclone characteristics of the 40-yr ECMWF Re-Analysis (ERA-40) are compared with the NCEP–NCAR dataset using one method. ERA-40 shows systematically more cyclones, and therefore a higher cyclone center density, than the NCEP–NCAR reanalysis dataset. Geostrophically adjusted geopotential height gradients around cyclone centers, a measure of cyclone intensity, are enhanced in ERA-40 compared with the NCEP–NCAR reanalysis dataset. The variability of the number of cyclones per season is significantly correlated between the two reanalysi…

Surface Cyclones in the ERA-40 Dataset (1958–2001). Part I: Novel Identification Method and Global Climatology

2006

Abstract A novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets. The method is used here to derive a climatology of extratropical cyclones from sea level pressure (SLP) fields. A simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local SLP minimum and is enclosed by the outermost closed SLP contour. This cyclone identification procedure can be applied to individual time instants, and climatologies of cyclone frequency, fc, are obtained by simple time averaging. Therefore, unlike most other climatologies, the method is not based on the application of…

Further examination of the thermodynamic modification of the inflow layer of tropical cyclones by vertical wind shear

2013

Recent work has developed a new framework for the impact of vertical wind shear on the intensity evolution of tropical cyclones. A focus of this framework is on the frustration of the tropical cyclone's power machine by shear-induced, persistent downdrafts that flush relatively cool and dry (lower equivalent potential temperature, θ<sub>e</sub>) air into the storm's inflow layer. These previous results have been based on idealised numerical experiments for which we have deliberately chosen a simple set of physical parameterisations. Before efforts are undertaken to test the proposed framework with real atmospheric data, we assess here the robustness of our previous res…

Identification and ERA-15 Climatology of Potential Vorticity Streamers and Cutoffs near the Extratropical Tropopause

2007

Abstract A novel approach is introduced to identify potential vorticity (PV) streamers and cutoffs as indicators of Rossby wave breaking near the extratropical tropopause and to compile climatologies of these features on different isentropic surfaces. The method is based on a contour searching algorithm that identifies the dynamical tropopause [2 potential vorticity units (PVU; PVU ≡ 1 × 10−6 K kg−1 m2 s−1) isoline] on isentropic surfaces. The contour is then analyzed to search for cutoffs and filament-like streamers. Whereas the identification of cutoffs is unambiguous, the one for streamers requires the specification of two parameters that determine the width and length of the contour fea…

Comparison of ERA40 cloud top phase with POLDER-1 observations

2008

[1] A detailed grid-point-based comparison of the cloud top phase derived from the 40-year reanalyses (ERA40) of the European Centre for Medium-Range Weather Forecasts (ECMWF) with satellite measurements is presented. For this purpose an algorithm is implemented to extract a two-dimensional “satellite-like” field of the cloud top phase from ERA40 data. This field is compared with cloud top phase data from the Polarization and Directionality of the Earth Reflectances (POLDER-1) instrument which was in orbit from November 1996 to June 1997. The thermodynamic cloud phase in ERA40 data is parameterized as a function of temperature with pure liquid clouds above 0°C, pure ice clouds below −23°C a…

Transport timescales and tracer properties in the extratropical UTLS

2010

A comprehensive evaluation of seasonal backward trajectories initialized in the northern hemisphere lowermost stratosphere (LMS) has been performed to investigate the factors that determine the temporal and spatial structure of troposphere-to-stratosphere-transport (TST) and it's impact on the LMS. In particular we explain the fundamental role of the transit time since last TST (tTST) for the chemical composition of the LMS. According to our results the structure of the LMS can be characterized by a layer with tTST<40 days forming a narrow band around the local tropopause. This layer extends about 30 K above the local dynamical tropopause, corresponding to the extratropical tropopause trans…

Identification of Tropical‐Extratropical Interactions and Extreme Precipitation Events in the Middle East Based On Potential Vorticity and Moisture T…

2018

The authors wish to thank CRED, ECMWF, NASA, JAXA, and APHRODITE for providing their data sets, which are available under the following links; EM-DAT (http://www.emdat.be/), ERA-Interim (https://www.ecmwf.int/en/research/climate-reanalysis/era-interim), TRMM (https://pmm.nasa.gov/data-access/downloads/trmm), and Aphrodite (http://www.chikyu.ac.jp/precip/english/). We acknowledge the Israeli Atmospheric and Climatic Data Centre (IACDC), supported by the Israeli Ministry of Science, Technology and Space, for providing the Israel Meteorological Service (IMS) daily rainfall records as well as the Ministry of Environment, Water and Agriculture (MEWA) in the Kingdom of Saudi Arabia for providing …